This invention relates to polyamide-imide copolymers containing polyetherimides and to molding powders, molded articles and films prepared therefrom. Amide-imide copolymers are a relatively new class of organic compounds known for their solubility in nitrogen containing solvents when in the largely polyamide form. The major application of these amide-imide homopolymers has been as wire enamels. This is illustrated in U.S. Pat. Nos. 3,661,832 (1972), 3,494,890 (1970), and 3,347,828 (1967). Amide-imide homopolymers are not useful in molding applications since parts made from the form fissures, and in general their molecular weight is too low. Amide-imide copolymers have also been found useful for molding applications as shown in U.S. Pat. Nos. 4,016,140 (1977), U.S. Pat. No. 4,136,085 (1979), U.S. Pat. No. 4,313,868 (1982), and U.S. Pat. No. 4,309,528 (1982) which are incorporated herein by reference. These polyamide-imide copolymers are known for their outstanding strength, stiffness and heat resistance properties, but they are brittle materials. The art has been looking for improvements in the impact resistance and toughness of the polyamide-imide copolymer.
A method for improving toughness and impact resistance in thermoplastic polymers is the addition of an impact modifier or toughening agent to the polymer. An example of this is the use of polybutadiene with polystyrene in preparing high impact polystyrene. With polyamide-imide copolymers, however, it is necessary to subject the molded article to a heat curing cycle in order to complete the solid state polymerization and achieve the excellent mechanical properties. Consequently, it is essential that an additive or impact modifier does not impair the curing characteristics of the polyamide-imide copolymer and reduce its cured mechanical properties, particularly the flexural and heat deflection properties. The ideal toughening agent for these copolymers would be one which increases the toughness of the polymer but which does not reduce the polymer's strength, stiffness or heat deflection temperature.